Once the birds and snakes were gone, James transformed back. The fight had changed now; he knew Sirius well enough to know that they were intended to get away while he fought, but he wasn't about to leave his friend behind. He did move to the door, to the side of it just in case anyone else came in - not wanting to give them the advantage of hitting him with it - but he wasn't done fighting. He aimed hexes at the place where Sirius' movements indicated their opponent was, for as long as he dared without worrying that he would hit his friend instead.